This project focuses on the postnatal development of central brain stem pathways associated with sensory input from the upper respiratory tract and with sleep and autonomic physiology. The project is designed to determine the synaptic development within the nucleus tractus solitarius, which is the primary sensory nucleus of the IX and the X nerves; the locus coeruleus which synaptically interacts with the nucleus tractus solitarius in autonomic function; and the gigantocellular tegmental field (FTG) of the pontine reticular formation, which is associated with rapid eye movement sleep. The synaptic development will be characterized 1) in the normal developing postnatal rat within the first two months following parturition, and 2) in the postnatal rat after repeated exposures to low levels of oxygen (hypoxia) during either prenatal or early postnatal periods. A stereological technique will be used to analyze large areas of the brain stem tissue by a nonbiased statistical method which allows the interpretation of the data within a three dimensional plane. This major technique will be supplemented by subjective analysis of the types of synapses as based on vesicular shape on both dendritic and somatic receptive fields. The purpose of the project is to determine if the neurons of these three regions undergo differential changes in synaptic contact with age.